fix(write-existing-file-guard): defer realpath/existsSync to first tool call

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/hooks/write-existing-file-guard/hook.ts

@@ -76,7 +76,15 @@ export function isOverwriteEnabled(value: boolean | string | undefined): boolean
 export function createWriteExistingFileGuardHook(ctx: PluginInput): Hooks {
   const readPermissionsBySession = new Map<string, Set<string>>()
   const sessionLastAccess = new Map<string, number>()
-  const canonicalSessionRoot = toCanonicalPath(resolveInputPath(ctx, ctx.directory))
+  let canonicalSessionRoot: string | undefined
+
+  function getCanonicalSessionRoot(): string {
+    if (!canonicalSessionRoot) {
+      canonicalSessionRoot = toCanonicalPath(resolveInputPath(ctx, ctx.directory))
+    }
+
+    return canonicalSessionRoot
+  }
 
   return {
     "tool.execute.before": async (input, output) => {
@@ -86,7 +94,7 @@ export function createWriteExistingFileGuardHook(ctx: PluginInput): Hooks {
         output,
         readPermissionsBySession,
         sessionLastAccess,
-        canonicalSessionRoot,
+        getCanonicalSessionRoot,
         maxTrackedSessions: MAX_TRACKED_SESSIONS,
       })
     },

src/hooks/write-existing-file-guard/lazy-canonical-path-init.test.ts

@@ -59,7 +59,7 @@ describe("createWriteExistingFileGuardHook", () => {
     ).rejects.toThrow("File already exists. Use edit tool instead.")
 
     // then
-    expect(existsSyncMock).toHaveBeenCalledTimes(2)
+    expect(existsSyncMock).toHaveBeenCalledTimes(3)
-    expect(realpathNativeMock).toHaveBeenCalledTimes(1)
+    expect(realpathNativeMock).toHaveBeenCalledTimes(2)
   })
 })

src/hooks/write-existing-file-guard/tool-execute-before-handler.ts

@@ -90,10 +90,10 @@ export async function handleWriteExistingFileGuardToolExecuteBefore(params: {
   output: { args?: unknown }
   readPermissionsBySession: Map<string, Set<string>>
   sessionLastAccess: Map<string, number>
-  canonicalSessionRoot: string
+  getCanonicalSessionRoot: () => string
   maxTrackedSessions: number
 }): Promise<void> {
-  const { ctx, input, output, readPermissionsBySession, sessionLastAccess, canonicalSessionRoot, maxTrackedSessions } = params
+  const { ctx, input, output, readPermissionsBySession, sessionLastAccess, getCanonicalSessionRoot, maxTrackedSessions } = params
   const toolName = input.tool?.toLowerCase()
   if (toolName !== "write" && toolName !== "read") {
     return
@@ -107,6 +107,7 @@ export async function handleWriteExistingFileGuardToolExecuteBefore(params: {
   }
 
   const resolvedPath = resolveInputPath(ctx, filePath)
+  const canonicalSessionRoot = getCanonicalSessionRoot()
   const canonicalPath = toCanonicalPath(resolvedPath)
   if (!isPathInsideDirectory(canonicalPath, canonicalSessionRoot)) {
     return